Efficient pre-distorted 12/4 QAM modulator

A method for predistorted 12/4-Quadrature Amplitude Modulation (QAM) comprising:

• selecting desired points on a 12/4 QAM constellation;
• mapping an input signal to a plurality of modulator control bits, the mapping determined by the selected desired points;
• phase shifting a continuous wave (CW) signal, the phase shifting being controlled by at least one of the plurality of modulator control bits;
• splitting the phase shifted CW signal into a first phase shifted CW signal and a second phase shifted CW signal;
• performing quaternary phase shift keying (QPSK) modulation on the first phase shifted CW signal and the second phase shifted CW signal, each QPSK controlled by two of the plurality of modulator control bits;
• attenuating the first QPSK modulated CW signal;
• and
• summing the attenuated QPSK modulated CW signal to the second QPSK modulated CW signal, the sum being a predistorted 12/4-QAM signal with the desired points.

A predistorted 12/4 Quadrature Amplitude Modulation (QAM) modulator comprising:

• a first phase shift module, the first phase shift module receiving an input signal and a fifth modulator control;
• a second phase shift module operatively connected to an output of the first phase shift module, the second phase shift module receiving a sixth modulator control bit;
• a first QPSK module operatively connected to an output of the second phase shift module, the first QPSK module receiving a phase shifted signal from the second phase shift module, the first QPSK module receiving a first modulator control and a second modulator control bit;
• a second QPSK module operatively connected to the output of the second phase shift module, the first QPSK receiving the phase shifted signal from the second phase shift module, the second QPSK module receiving a third modulator control bit and a fourth modulator control bit;
• a variable attenuator, the variable attenuator operatively connected to the second QPSK module;
• and
• a summer operatively connected to the first QPSK module and the variable attenuator, the summer producing a 12/4-QAM signal by adding a QPSK signal from the first QPSK module with an attenuated signal from the variable attenuator, and
• wherein an input signal is mapped to the first modulator control bit, second modulator control bit, third modulator control bit, fourth modulator control bit, fifth modulator control bit, and sixth modulator control bit based on desired points on a 12/4 QAM constellation, the first modulator control bit, second modulator control bit, third modulator control bit, fourth modulator control bit, fifth modulator control bit, and sixth modulator control bit controlling the 12/4 QAM modulator to produce the desired points on the 12/4 QAM constellation.

A pre-distorted QAM modulator comprising:

• a phase shift module operating at a modulator symbol rate, the phase shift module receiving an input signal;
• at least two quaternary phase shift keying modules operating at the modulator symbol rate, the at least two quaternary phase shift keying modules operatively connected to the phase shift module, each at least two quaternary phase shift keying modules receiving a different portion of a signal from the phase shift module, the phase shift module and the quaternary phase shift keying modules receiving at least one nonreturn-to-zero (NRZ) symbol input;
• a variable attenuator device operatively connected to one of the quaternary phase shift keying modules;
• a summer operatively connected to the quaternary phase shift keying modules, the summer producing a modulator output signal by adding output signals from the quaternary phase shift keying modules, wherein the modulator output signal is a pre-distorted QAM modulation for the at least one NRZ symbol that compensates for amplitude compression due to distortion from a nonlinear element between the modulator output signal and a demodulator.

A method for pre-distorted QAM modulation comprising:

• receiving a carrier signal and at least one input symbols;
• phase modulating the carrier signal at an input symbol rate;
• splitting the phase modulated carrier signal into parts;
• modulating each phase modulated carrier signal part at the input symbol rate using quaternary phase shift keying;
• attenuating one of the quaternary phase shift keying modulated phase modulated carrier signal parts;
• summing the attenuated one of the quaternary phase shift keying modulated phase modulated carrier signal parts with each other quaternary phase shift keying modulated phase modulated carrier signal part,
• wherein the summing produces a pre-distorted QAM modulation for at least one input symbol that compensates for amplitude compression due to amplifier nonlinear distortion.

A predistorted 12/4 Quadrature Amplitude Modulation (QAM) modulator comprising:

• a mapping device mapping a modulator input bits to a plurality of nonreturn-to-zero (NRZ) modulator control bits, the mapping being determined by selected desired points on a 12/4 QAM constellation;
• at least two quaternary phase shift keying (QPSK) modulators, each QPSK modulators receiving a portion of an input signal, each QPSK modulator receiving NRZ modulator control bits;
• an attenuator, attenuating a first QPSK signal outputted from a first of the QPSK modulators;
• a summer, adding the attenuated first QPSK modulated signal with a second QPSK modulated signal, the second QPSK modulated signal being outputted from a second of the QPSK modulator;
• a first phase shift device, the first phase shift device receiving an output signal from the summer and at least one of the plurality of NRZ modulator control bits;
• and
• a second phase shift device, the second phase shift device receiving an output signal from the first phase shift device and at least one of the plurality of NRZ modulator control bits, the second phase shift device outputting a predistorted 12/4 QAM signal,
• wherein the plurality of modulator control bits control the first phase shift device, the second phase shift device, and the two QPSK modulators to achieve the desired points on the 12/4 QAM constellation.

A predistorted 12/4 Quadrature Amplitude Modulation (QAM) modulator comprising:

• a mapping device mapping a modulator input bits to a plurality of nonreturn-to-zero (NRZ) modulator control bits, the mapping being determined by selected desired points on a 12/4 QAM constellation;
• a first phase shift device, the first phase shift device receiving an input signal and at least one of the plurality of NRZ modulator control bits;
• at least two quaternary phase shift keying (QPSK) modulators, the QPSK modulators receiving phase. shifted signals from the first phase shift device, each QPSK modulator receiving NRZ modulator control bits;
• an attenuator, attenuating a first QPSK signal outputted from a first of the QPSK modulators;
• a summer, adding the attenuated first QPSK modulated signal with a second QPSK modulated signal, the second QPSK modulated signal being outputted from a second of the QPSK modulator;
• and
• a second phase shift device, the second phase shift device receiving an output from the summer and at least one of the plurality of NRZ modulator control bits, the second phase shift device outputting a predistorted 12/4 QAM signal,
• wherein the plurality of modulator control bits control the first phase shift device, the second phase shift device, and the two QPSK modulators to achieve the desired points on the 12/4 QAM constellation.

A method for predistorted 12/4-Quadrature Amplitude Modulation (QAM) comprising:

• selecting desired points on a 12/4 QAM constellation;
• mapping an input signal to a plurality of modulator control bits, the mapping determined by the selected desired points;
• phase shifting a continuous wave (CW) signal, the phase shifting being controlled by at least one of the plurality of modulator control bits;
• splitting the phase shifted CW signal into a first phase shifted CW signal and a second phase shifted CW signal;
• performing quaternary phase shift keying (QPSK) modulation on the first phase shifted CW signal and the second phase shifted CW signal, each QPSK controlled by two of the plurality of NRZ modulator control bits;
• attenuating the first QPSK modulated CW signal;
• and
• summing the attenuated first QPSK modulated CW signal to the second QPSK modulated CW signal;
• and
• phase shifting the sum of the attenuated first QPSK modulated CW signal, the phase shifting being controlled by at least one of the plurality of modulator control bits, the phase shifting producing a predistorted 12/4-QAM signal with the desired points.

A method for predistorted 12/4-Quadrature Amplitude Modulation (QAM) comprising:

• selecting desired points on a 12/4 QAM constellation;
• mapping an input signal to a plurality of modulator control bits, the mapping determined by the selected desired points;
• splitting a continuous wave (CW) signal into a first CW signal and a second CW signal;
• performing quaternary phase shift keying (QPSK) modulation on the first CW signal and the second CW signal, each QPSK controlled by two of the plurality of modulator control bits;
• attenuating the first QPSK modulated CW signal;
• and
• summing the attenuated first QPSK modulated CW signal to the second QPSK modulated CW signal;
• and
• phase shifting the sum of the attenuated first QPSK modulated CW signal and the second QPSK modulated CW signal, the phase shifting being controlled by at least one of the plurality of modulator control bits, the phase shifting producing a predistorted 12/4-QAM signal with the desired points.